The present invention relates to an eye direction detecting device which is, for example, employed in a finder system of a camera, for detecting a direction to which a user's eye is directed within the finder,
A conventional eye direction detecting device is disclosed in, for example, U.S. Pat. No. 5,327,191, corresponding to Japanese Laid-open Patent Publication No. HEI 2-5. The eye direction detecting device disclosed in these documents utilize a light projection system that projects illumination light along an optical axis of a finder system, as a parallel luminous flux, toward an eye of a user. The finder system has an eyepiece with a coaxial optical axis, a light receiving system with a light receiving element that outputs a signal corresponding to a light distribution of light reflected from the eye, and a calculation device that processes the output from the light receiving system to detect a direction of the eye.
In this conventional device, the light receiving system and the finder system have coincident optical axes, so that the eye direction of a user viewing a scene through the finder is detected. Furthermore, in this conventional device, the light projection system disclosed therein projects illumination light along the optical axis of the finder system, and illumination light enters the eye even when the eye is moved along the optical axis of the finder system.
In this conventional device, a portion of the emission light is regulated by the cornea, and forms a first Purkinje image on the light receiving element. A portion of the illumination light also reaches the retina through the pupil of the eye, and the reflected component of the light from the retina also forms an image on the light receiving element. The calculating device calculates the separation distance between the center of the pupil and the first Purkinje image using the light distribution from the light receiving element, and calculates an angular displacement of the user's eye eyeball using the above-mentioned separation distance and a predetermined distance between the center of the pupil and the center of curvature of the cornea.
However, according to this conventional eye direction detecting device, when a photographer wears eyeglasses, a strong reflection component from the eyeglasses interferes with the reflection components from the eyeball, and separation of the eyeglass component from the eye component is difficult. Accordingly, the detection of eye direction may be inaccurate or impossible.
Further, in the conventional device, the pupil center location is calculated using the component reflected by the retina. In this case, the strength of the retina-reflected component changes depending on the position of the eye and/or the ambient brightness, resulting in a lack of precision in the pupil center calculation and other calculations derived therefrom.
In an alternative known structure, the illumination light is provided by a source away from the optical axis of the finder system. In such a case, illumination light is emitted at a wide angle, so that sufficient light enters the eye even when the eye moves in the optical axis direction. Since the light source illuminates in a wide angle to all directions of the light projection system, only a small amount of the total light available enters the eye, and the remainder is not used. For example, when a light source is provided away from the optical axis of the finder at the lower side, a user's eye looking into the finder is positioned above the light source. Most of the illumination light is directed away from entering the eye, and is thereby wasted. A strong, and therefore large, light source, or multiple light sources, are therefore necessary to achieve a satisfactory signal strength from the sensor.